Since their inception, semiconductor devices have played an important role in the technological development of industries and societies. From the first solid state radio, semiconductor devices have evolved in design and application to contemporary computer systems, cellular telephones, radar systems, medical instrumentation, and household appliances. However, the evolution of semiconductor devices was not instantaneous.
Early semiconductor devices were passive and limited to simple junction (i.e., pn junction) devices known as diodes. These simple junction devices, in turn, lead to the development of other devices, such as transistors and integrated circuits. These early semiconductor devices were packaged in epoxies or plastics and had only two or three metal leads for electrical connection.
As the art continues to evolve, complex semiconductor devices are now required in many applications. These complex devices must be capable of operating over a broad frequency and power range. For example, cellular telephones and radar systems require semiconductor devices having high frequency and high power capabilities. Consequently, specialized packages are needed to house these semiconductor devices. These semiconductor packages must be capable of withstanding a plurality of environmental and physical challenges while at the same time providing the packaged semiconductor device with proper electrical connectivity to the outside world.
Because these complex semiconductor designs require a large number of electrical connections to circuitry outside of the semiconductor's package, the semiconductor's package must be constructed with one or more electrical feedthroughs. An electrical feedthrough is a device for providing electrical connectivity between a packaged semiconductor device and external circuitry. Electrical feedthroughs must be particularly constructed with many layers of materials so as to provide insulation from the external housing of a semiconductor package and yet still provide the semiconductor package with the ability to withstand environmental and physical challenges. However, due to this particular construction, it has been heretofore difficult to create hermetic seals in electrical feedthroughs and packages.
A hermetic seal is a seal which does not allow the passage of fluids, including air, through its confines. Prior attempts at forming hermetic seals suffered from a warping or "potato chip" effect which describes a great variance in the structural uniformity of a sealing assembly caused by employing a great number of material layers in the assemblage. Furthermore, these attempts did not consistently result in hermetic seals. Yet other attempts at forming hermetic seals provided fragile sealing assemblies which quickly developed leaks upon minor physical stressing. Accordingly, a method for creating hermetic seals is desirable which does not suffer from the aforementioned defects.